1. Field of the Invention
The present invention relates to an ultrasonic wire bonding apparatus, and more particularly to a transducer control circuit utilized in such an apparatus.
2. Prior Art
In ultrasonic wire bonders, a bonding tool is attached to the tip of a transducer which generates ultrasonic waves, and a wire bonder is used with a bonding wire passed through this bonding tool. The transducer is lowered so that the bonding wire is pressed against a bonding point by the bonding tool and the bonding wire is bonded to the bonding point by the ultrasonic waves generated from the transducer.
When such transducers are manufactured, there are measurable differences in the characteristics depending upon the quality of the materials used and the precision of working, even though it is desirable to manufacture transducers having identical characteristics. Accordingly, if only transducers with more or less identical characteristics are wanted, all of the transducer whose characteristics show a considerable degree of variance from the selected norm are wasted, thus increasing the unit cost of the product.
In cases where transducers having different characteristics are used, the transducers show different current values even though the same voltage is applied, resulting in different oscillation amplitudes. This causes differences in the pressure bonding strength (the strength with which the bonding wire is pressure-bonded to the bonding point), improper bonding of the bonding wire, etc.
Furthermore, in cases where the same bonding sample is bonded using a multiple number of ultrasonic bonding wire bonders, the bonding work can be performed quickly by setting the necessary data concerning the bonding conditions (e.g., bonding coordinates, ultrasonic oscillating output, ultrasonic oscillation time, bonding load, looping height, etc.) in one of the wire bonders and transferring this data to the other wire bonders, so long as the characteristics of the respective wire bonders are uniform. However, if the transducer characteristics are different, uniform data such as the ultrasonic oscillating output and time requirements cannot be obtained. As a result, bonding work cannot be performed using the same date in respective wire bonders. In other words, it becomes impossible to transfer the bonding conditions from one bonder to another. Thus, bonding condition data must be individually set for each wire bonder.